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DDTThis week’s Spinneret post actually points you to my latest Alchemist column on ChemWeb.com but also goes into a little more detail on one of the items reported there regarding pesticide contamination.

Read the extra details on chemical sensitivityhere.

One Response to “Chemical Sensitivity”

Follow-up comment via email from Dan Lednicer whose original email inspired this post:

My comments reflected the four years that I worked in a contract analytical firm rather than personal criticism. A good many of our contracts involved determination of levels of drugs in serum samples from clinical trials. Since the data were intended to support the New Drug Application to be filed with FDA analyses were carried out with exceedingly stringent operating procedures.

A typical day’s run was preceded by determination of a calibration curves, this comprised injection of seven samples extracted from spiked serum samples in exactly the same manner as samples from the trial. (If this did not yield a correlation coefficient of .995, it was back to the drawing board). Samples of spiked with known concentrations of drug were randomly interspersed among real samples when it came time for the actual analytical work so that no more than five consecutive shots consisted of unknowns.

Many of the assays we carried out were linear down to the level for nanograms/mL. Though we could sometimes see even lower levels those data could not be used as they were beyond the linear range. Preparation of pefluorinated derivatives (i.e. heptafluorobutyric ester or amide) not only increased detector sensitivity but also increased ‘€œvolatility’, lowering retention time.

Much the same protocol applied to HPLC assays, though in this case sensitivity to halogen did not apply.

Dan